Field of the Invention
The present invention relates to an expansion sheet adapted to be expanded in the condition where a platelike workpiece is attached to the expansion sheet, and also relates to a manufacturing method for the expansion sheet and an expanding method for the expansion sheet.
Description of the Related Art
As a method for dividing a platelike workpiece such as a semiconductor wafer into a plurality of chips, there has been put into practical use a processing method including the steps of focusing a laser beam inside the workpiece to thereby form a modified layer (modified region) inside the workpiece and next applying an external force to the workpiece to divide the workpiece along the modified layer (see Japanese Patent Laid-open No. 2002-192370, for example). In this processing method, an expansion sheet attached to the workpiece is expanded to thereby apply an external force to the workpiece, thus dividing the workpiece into the plural chips.
As another method, there has been proposed a processing method utilizing an external force applied to the workpiece in grinding or polishing the workpiece after forming a modified layer inside the workpiece, thereby dividing the workpiece along the modified layer into the plural chips (see PCT Patent Publication No. WO2003/77295, for example). After dividing the workpiece into the plural chips in this processing method, the expansion sheet attached to the workpiece is expanded to increase the spacing between any adjacent ones of the plural chips. In this case, it is possible to prevent damage to each chip due to the contact of the adjacent chips in handling each chip later.
In recent years, there has been put into practical use an expanding apparatus capable of expanding an expansion sheet in desired directions (see Japanese Patent Laid-open No. 2014-22382, for example). This expanding apparatus includes a first holding unit (first holding means) and a second holding unit (second holding means) opposed to each other with a workpiece interposed therebetween in a first direction substantially parallel to the expansion sheet, in the condition where the workpiece is attached to the expansion sheet. The expanding apparatus further includes a third holding unit (third holding means) and a fourth holding unit (fourth holding means) opposed to each other with the workpiece interposed therebetween in a second direction perpendicular to the first direction in a plane parallel to the expansion sheet. The first holding unit and the second holding unit are movable away from each other in the first direction, and the third holding unit and the fourth holding unit are movable away from each other in the second direction. These four holding units are operated to hold four areas of the expansion sheet. Thereafter, the first holding unit and the second holding unit are moved away from each other in the first direction, and the third holding unit and the fourth holding unit are moved away from each other in the second direction, so that the expansion sheet can be expanded both in the first direction and in the second direction.